Colorado fell under several governmental jurisdictions during its developmental history, being for a time part of the territories of Spain, Missouri, Mexico, Utah, the United States, New Mexico, unorganized Native American land, and finally Nebraska and Kansas. Non-federal records, however, exist only for the domains of Utah, New Mexico, Kansas, and Nebraska territories. The territory of Colorado, with its seventeen counties, was formed in 1861. Sixteen years later, on 1 August 1876, it was admitted as the thirty-eighth state in the Union.

Bent’s Fort, built in 1833 and now a national historic site near La Junta, established an extensive trading system between Native Americans and fur trappers, but the San Luis Valley was the site of the first permanent nonnative settlement in what became Colorado, with the town of San Luis being founded in 1851. One year later, Fort Massachusetts, later replaced by Fort Garland, was erected on the Ute Creek to protect travelers on the Santa Fe Trail. At that time most pioneers were not settling in Colorado but rather moving through to California and Oregon.

Mining accounted for the first extensive settlement around what is now Denver. Reports of gold began in the spring of 1858 and brought many newcomers to the area. Later that year the “Pike’s Peak or Bust” gold rush began, and in 1859 a “Second Stampede” brought additional thousands searching for gold, including both settlers and speculators. Within only a few years, however, the population began to shift from speculator to settler. The 1860 territorial census of Colorado counted 32,654 white males and 1,577 white females, but by May 1861 the census taken by Territorial Governor William Gilpin counted 20,798 males and 4,484 females. Clearly, as the men were moving on to other ventures, the type of people coming to Colorado began to change.

Early native tribes in Colorado included the Ute, the Apache, and “the wandering tribes” of Cheyenne, Arapaho, and Sioux. On 18 February 1861, the Cheyenne and Arapaho negotiated a treaty at Fort Wise, Kansas, in which they ceded all lands in the Pike’s Peak region to the United States. A treaty with the Ute followed in 1864, ceding all Ute land east of the Continental Divide. Despite the treaties, the period from 1861 to 1864 was a time of enormous tension between natives and the settlers. Before the Sand Creek massacre in November 1864 there were numerous raids and killings. By 1881 the Ute Indians completed moving from the western part of the state into Utah, and large sections of Colorado became open for settlement.

During the Civil War, over 8,000 men served in Colorado units. Many Northerners living in Colorado returned to their prior residences in other states to help fight for the Union cause, while some settlers remained in their new domicile. Colorado participated in a major battle in the Civil War that occurred in March 1862 when Governor Gilpin organized one of three Colorado companies to stop the Confederate attempt to block the western supply of gold to the eastern states. Forces clashed at Glorieta Pass, New Mexico, and the Confederates retreated.

After the Civil War, the population of Colorado began to expand primarily through the development of railroads. The first “Iron Horse” arrived in Denver on 24 June 1870. The researcher with early Colorado ancestors should therefore watch for migration during the 1870s and follow the growth of the railroads. A promotional organization, the Colorado Board of Immigration, was created in 1872, and the population of Colorado tripled between 1870 and 1875. Unfortunately, this decade also brought grasshoppers and economic depression, forcing many settlers to return to the East or go farther west. Throughout these difficult times, mining and agriculture remained the two important industries.

Most migration to Colorado came from a block of states extending from New York and Pennsylvania on the east to Kansas and Nebraska on the west. In 1860 the greatest number of immigrants to Colorado came from Ohio, followed by Illinois, New York, Missouri, and Indiana. The population explosion after the Civil War brought native-born Americans primarily from the states of Missouri, Kansas, Nebraska, and Iowa. The population of Colorado also included a large number of foreign-born immigrants including Czechs, Slovaks, Irish, Germans, Russians, Canadians, Swedish, Scots, Italians, and Chinese. By 1880, one-fifth of the population of Colorado was foreign-born and the state had three official languages: English, Spanish, and German. In the 1890s more Germans arrived, an ethnic group that continues to dominate in eastern Colorado today.